Method and apparatus for treating boards molded of fibrous material



July 17, 1956 J. D'A. CLARK 2,754,540

METHOD AND APPARATUS FOR TREATING BOARDS MOLDED OF FIBROUS MATERIAL,EgQZ

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United States Patent METHOD AND APPARATUS FOR TREATING BOARDS MOLDED OFFIBROUS MATERIAL James dA. Clark, Longview, Wash.

Application August 18, 1952, Serial No. 304,923

11 Claims. (Cl. 18--1) This invention relates to the manufacture ofpanels, boards and the like molded of fibrous elements, such as woodywafers or cellulose fibers and it relates more particularly to apparatusand to a method for treating such structures immediately subsequent totheir molding operation for the purpose of improving their resistance towater and the strength properties of the molded products and tocondition the boards for better dimensional stability.

Various techniques for the heat treatment of boards subsequent tomolding have been tried but the difiiculties involved have scarcely beenjustified by the minor improvements secured in the molded products andthe great majority of such techniques have thus been abandoned. In oneprocess, generally referred to as hot stacking, the boards are piled oneon top of the other as they issue from the hot molding press. While someof the heat of the molding operation remains in the boards, much thereofis lost into the atmosphere since the board last to issue is placed ontop of the stack where heat losses are maximum. As a result, the averagetemperature of the boards in the stack is relatively low so that little,if any, beneficial changes are secured and any such changes vary incharacter throughout the stack because the last boards are subject to aconsiderably less intense treatment than the boards in the bottomportion of the stack.

The need for a practical solution to a subsequent treatment of moldedboards for the purpose of improving moisture resistance and dimensionalstability becomes particularly important in the recent development ofdry molded boards having very little, if any, additional resinousbinder, such as is described in my copending application Serial No.192,284, filed on October 26, 1950, now abandoned. It has been foundthat boards molded by the dry process described to a medium density ofabout 0.6 to 0.9 will not have a high degree of moisture resistanceunless a high concentration of wax is employed as a size for the fibers.When hydrophobic waxes are present in sufficient quantity to impart ahigh resistance to moisture, the bonding relation between fibrouselements becomes markedly reduced and a molded product of relatively lowstrength results. The usual method of hot stacking previously describedprovides some improvement in water resistance but scarcely sufficient tojustify the effort. Preheating of the fibrous elements to temperaturesup to 350 F. improves water resistance but the strength of the productmolded therefrom is then thereby considerably decreased.

It is an object of this invention to provide a method and apparatus forthe treatment of boards molded of fibrous material for the purpose ofincreasing their water resistance without loss of strength and it is apreferred object of this invention to provide a new and improved methodand apparatus for the heat treatment of boards subsequent to moldingwhereby their moisture resistance is increased and their strengthproperties are also increased in a practical and an economical manner.

It is another object to provide a heat treatment of the 'ice 2 typedescribed which makes sufficient use of the heat remaining in the boardssubsequent to molding and subjects each board to substantially identicalaging conditions to equalize their properties prior to conditioning theboards to become in equilibrium with the ambient atmosphere.

A further object is to provide an effective and economical system forgreatly improving the resistance of the fibrous molded board to waterand to minimize dimensional changes and Warping responsive to changes inambient atmospheric conditions.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, embodiments of the invention are shown in the accompanyingdrawing in which- Figure l is a plan view of a system for handlingmolded boards in accordance with the practice of this invention;

Figure 2 is an elevational view in section showing in detail a hotstacker embodying features of this invention;

Figure 3 is an enlarged sectional elevational view of a portion of thehot stacker;

Figure 4 is a fragmentary sectional elevational view of a modificationin a hot stacker embodying features of this invention, and

Figure 5 is a sectional elevational view of a modified form of platen ortable.

It has been found that in dry molding, boards of the type described maybe greatly improved in their water resistance and dimensional stabilitywhile also increasing the strength properties thereof when such boardsare conditioned at a temperature ranging from about 230 to 360 F. underslight pressure subsequent to molding for from several hours to abouthalf an hour for the highest temperature. and it is an object of thisinvention to provide means for expediently subjecting the boards to theconditions described in an economical and uniform manner.

In accordance with the practice of this invention there is provided anew and improved hot stacking apparatus operating on a principle unlikethat which has heretofore been employed in the molding industry. Insteadof removing the hot molded boards and piling them one on top the otherwhere the heat can radiate therefrom rapidly to reduce the effectivetemperature and thereby markedly reduce the average temperature of theboards in the pile, an improved hot stacker is provided wherein theboards last removed from the molding press are fed from the bottom intothe pile and the bottom of the pile rests on a hot plate which not onlyinsulates the boards against heat loss but supplies additional heat fromits surface. By displacing boards upwardly from the bottom and removingthe heat treated boards from the top, each board is subjected tosubstantially identical temperature, time, and pressure conditionswhereby greater uniformity exists in the final products.

My new and improved hot stacker comprises a pair of feed rolls 10 and 11for advancing boards 12 onto the upper surface of a hot plate 13dimensioned to correspond in size and shape to the molded boards. Thehot plate is channeled for heating by hot water or steam or byelectrical resistance units. The hot plate is sup ported on a pluralityof spaced cross beams 14 and iongitudinal beams 15 forming a tableadapted to be actuated vertically between a raised and a loweredposition of adjustment by suitable actuating means, such as the cams 16mounted on rotatable shafts 22. The shafts are adapted to be turned by amotor 23 having a drive shaft 24 operatively connected to shafts 22 by aworm and worm gear arrangement. It will be understood that other meanswell known in the industry for actuating such units in vertical movementmay, in the alternative, be

3 used, such for example as hydraulically operated rams or the like.

The stacker in which the boards are aged under heat and pressure toimprove the physical properties thereof comprises a rectangular housing25 preferably formed of heat insulating side walls 26 which may also beprovided with heating elements therein for the purpose of maintainingthe desired temperature and the housing is dimensioned to conform insize and shape to the boards adapted to be stacked therein. The housingis open at its upper end to permit removal of the uppermost board as bya lift having a vacuum cup 27 to grip the face of the board, or removalmay be effected by other means. The housing is also open at an end nearthe bottom to admit boards subsequently advanced therein over the hotplate 13. The stack of boards is supported within the housing by the hotplate which ordinarily forms its bottom wall or by removable shelvesoperating in timed relation with the movement of the hot plate. Theshelves move into position of support in advance of withdrawal of thehot plate for reloading with more boards for the hot stacker.

While description will be made to the holding assembly associated withone side wall of the housing, it will be understood that a similarassembly is provided with both side walls for operation in the mannerdescribed in cooperation with the housing and board feeding means.Aligned with the underside of the housing wall and preferably positionedto form a continuance thereof is an elongate structural member of highstrength, such as an angle iron 28 supported at its underside by aplurality of upright rigid columns 29 pivoted at their lower end onbrackets 30 for rocking movement in the direction toward and away fromthe wall. Secured to the underside of the angle iron 28 is a shelf plate31 which extends a short distance into the opening defined by thehousing to engage the underside of the lowermost board in the stack andprovide a rest therefor. If the boards are trimmed to the width of thehot plate, the underside of the shelf is chamfered as at 32 in its outerend portion to cooperate with a chamfered side edge 33 of the hot plateto permit movement of the shelves into position to engage the undersideof the lowermost board for support thereof in advance of withdrawal ofthe hot plate to retracted position. Otherwise, if untrimmed, the sidesof the boards overlap the sides of the hot plate as shown in Figure 4.In such instance it is preferred to have the hot plate 50 dimensioned tobe less than the distance between the chamfercd edges 32 of the shelfplates 31 and the edges of the hot plate need not be chamfered forcooperation therewith.

Normally the columns 29 are adapted to be rocked outwardly to displacethe shelves from the housing opening as the hot plate or table rises toposition operatively to engage the lowermost board in the stack andsupply the support therefor. Such rocking movement in timed relationwith the hot plate is achieved by an operative connection with the camsand a lever assembly 34 operatively engaging the columns at anintermediate portion thereof as by means of a lug 16 on the cam 16 whichis adapted to engage a projection 29" fixed to the arm 29 and lying inthe path of the lug 16 during rotation of the cam 16 to raise the table13. Such lever assembly may include a horizontally disposed lever 35pivoted at one end on an car 36 fixed to the column while the other endis pivoted at the upper end of a vertically disposed lever 37 pivoted atits lower end upon an car 38 fixed to a stationary frame member 39.

In operation, when the boards 12 are removed one at a time or in groupsfrom the hot molding press, they are stacked on a roller conveyor 40 orother conveying means or by a suitable pusher means to between rollers41 and 42 located at the end thereof for feeding the boards between apair of saws 43 which trim the boards to desired dimension. From thetrimming saws, the

4- boards 12 are advanced in substantially continuous fashion bycooperating rollers 44 and 45 to another roller conveyor 46 or the likeinto feeding relation with the rollers 10 and 11 of the described hotstacker. If desired, the rolls 41, 42, 44 and 45 and the saws 43 may bedispensed with and the untrirnmcd boards fed directly between rolls 10and 11.

Normally the hot plate 13 is in its raised position of adjustment andfunctions as the bottom wall of the housing to support the boardstherein while also imparting heat to the lowermost board for assistancein compensating for heat losses and to maintain a high temperature levelwithin the housing. When it is desired to lower the hot plate forreceiving additional boards to be inserted within the stacker, thecolumns 29 and the attached shelves 31 are rocked to their operativeposition of adjustment whereby the edge portion 32 cooperates with theedge 33 of the hot plate to permit movement of the shelves into positionof use supporting the stack of boards within the housing in advance ofremoval of the hot plate from its raised position of adjustment. Uponremoval, it will be apparent that at least the bottommost group ofboards will be flexed to some degree, as indicated by the broken linesin Figure 2 as their center support is withdrawn. Such flexing action,especially with certain board constructions, such as facing the lowersurface of the board with a veneer having its grain parallel to thelength of the board, has been found most desirable in relieving strainsand stresses existing within the board structures. With other boardconstructions, the boards may be flexed upwardly by providing a hotplate 51 with a cylindrical convex surface 52, as shown in Figure 5.

When in their lowered position of adjustment, the feed rollers 10 and 11are operated to advance the boards over the roller conveyor onto theupper surface of the hot plate until stopped in properly alignedposition by the stop plate 47. Then the table is cammed to its raisedposition of adjustment in cooperation with mechanism operativelyconnected thereto for withdrawing the shelves 31 from the path of theboards as they are carried into the housing to displace the stackupwardly therein. As previously pointed out, the uppermost boards in thestack have been subjected while in the hot stacker to an averagetemperature in the order of 230 to 360 F. It will also be obvious thatthe boards, as they are introduced and while they are in the hottest andmost reactive conditions are subject to maximum pressures comprising thecumulative weight of the boards positioned thereover in the stack andthat such boards continue to be under pressure though of lessermagnitude as the boards continue to rise by displacement upwardlythrough the stacker. Under such conditions, it has been found thatmarked improvement is not only secured in the resistance to water and towarpage but that the strength and other physical properties of theboards are increased. Some darkening of the boards usually takes placeunder the conditions of hot stacking described but the boards which areto be used in exposed areas are usually faced with a surface ply or thelike which completely conceals any imperfections or undesirablediscoloration.

As the boards are raised above the level of the housing or into theupper portion thereof, a pusher mechanism may be used for displacementof the boards onto a conveyor for storage or a suction device of thetype described may be used to lift the boards out of the stacker one ata time for displacement to storage or packing devices. At this stage,the uppermost board is relatively cool and capable of being handled.

As a rule, the hot stacker is used in conjunction with a hot press forconsolidating fibrous elements into panels, boards and the like. It isdesirable to effect the transfer !of the boards to the stacker asquickly as possible so that the major portion of the heat introducedinto the board during molding may be maintained. That which avenue islost can be made up quickly such as by replacement of heat from the hotplate into the bottom surface of the lowermost board which is subject togreatest heat loss during transfer. Heat which is lost from the uppersurface of the top board during transfer to the stacker is also capableof being substantially completely replaced by the high temperaturesexisting on the underside of the lowermost board already in the stackerwhich has been in contact with the surface of the hot plate prior to itsbeing lowered for loading. Thus heat is reintroduced in the boards atplaces most needed; nevertheless, all of the boards soon becomeequalized substantially to uniform temperature in the stacker although atemperature gradient will exist from bottom to top.

By way of illustration, if four boards of about inch thickness aremolded on a 6-minute cycle and advanced as a group for hot stacking,boards totaling about 15 inches will be introduced into the stackerhourly. Thus in a stacker having a height of 60 inches, each board willbe subject to the temperature and pressure conditions therein for about4 hours. With boards molded of woody Wafers sized with 2 percent wax andbonded with about 1 /2 percent phenol formaldehyde resin, it has beenfound that a very desirable improvement in resistance to water issecuredin the hot stacker of the type described when subjected to an averagetemperature of about 360 F. for /2 hour or about 1 hour at 340 F. orfrom 2 to 4 hours at temperatures of 320 to 280 F. Additional time atthe temperature employed is helpful to relieve strains by further smallamounts through plastic flow which is believed to take placecontinually.

It will also be seen that by the practice of this invention, thenecessary dwell time in the press to set the resinous binder in themolded board may be reduced to a minimum relying upon the furtheradvancement of the resinous binder especially that in the center laminaof the board to the cured stage during the passage of the board throughthe hot stack. This advantage will accrue in addition to the improvementin water resistance and the equalization of forces within the boards sothat they are caused to lie flat with little or no tendency to warp ortwist. Reaction of the binder to an advanced stage of polymeric growthin the stacker and the action of heat upon the wood substance is alsoresponsible for an increase in strength in the final product. It ispossible that these improvements in characteristics with respect towater resistance, reduction in warpage and increase in strength might beaccomplished by reduction of pressure in the consolidating press andextending the molding cycle of the boards therein. However, this wouldreduce the output of the press to an impractical low value and would bemost undesirable.

If the side edges of the boards are not trimmed with the saws untilafter the hot stacking operation, they may collectively serve as a goodinsulating wall for the stack in place of or in addition to theinsulated walls 25, the only drawback being an increased stroke and biteof the side supporting members. In this case, the edges are permitted tooverlap the sides of hot plate 13 by about 2 inches and the stroke ofthe rocking arms increased by this distance.

It will be understood that various changes may be made in the details ofconstruction, arrangement and in operation without departing from thespirit of the invention, especially as defined in the following claims.

I claim:

1. The method of heat treating boards of fibrous material compoundedwith a thermosetting binder comprising the steps of placing a boardafter hot molding and while the board still retains much of its heat ona heated plate, separating the board from the plate, introducing asecond board therebetween to form a stack of boards, separating thelowermost board of the stack from the plate, introducing additional hotboards therebetween and continuing the separation of the stack and plateand t 6 r the introduction of additional boards until the stack is of adesired height, and thereafter removing a number of boards from the topof the stack corresponding to the number intermittently inserted beneathit to maintain the stack at the desired height whereby each board isgiven substantially the same heat treatment during its passage upwardsthrough the stack.

2. In the method of conditioning boards of fibrous material compoundedwith a thermosetting binder and molded under heat and pressure to anadvanced but incomplete stage of cure, the steps of conditioning theboards with heat, immediately after molding, in a hot stacker comprisingpositioning the boards immediately after moldingon a hot plate beforeappreciable amounts of heat from the molded board have escaped from thesurfaces thereof, bringing the hot plate and stacker together so thatthe hot plate forms the bottom wall of the stacker whereby the boards onthe hot plate are introduced into the bottom of the stacker fordisplacement of the others therein upwardly to form a pile in which theboards introduced form the bottom of the pile, supporting the pile ofboards in the stacker at the edge portion of the lowermost board whenthe stacker and hot plate are separated for receiving additional boardswhereby the pile of boards in the stacker flex downwardly through thecentral portions thereof, and removing a number of boards from the topof the pile corresponding to the number of boards introduced into thestacker to form the bottom of the pile.

3. The method as claimed in claim 2 which includes the additional stepof heating the boards by heating elements placed within the insulatingwalls surrounding the stack to maintain a temperature ranging from about260 to 380 F. in the stack.

4. In the method of conditioning boards of fibrous material compoundedwith a thermosetting binder and molded under heat and pressure to anadvanced but incomplete stage of cure, the steps of conditioning theboards with heat immediately after molding in a hot stacker comprisingpositioning the molded boards on a heated platen before appreciableamounts of heat from the molded boards have escaped from the surfacesthereof, introducing the boards on the heated platen into the bottom ofthe stacker whereby the boards introduced into the stacker form a pilewith the boards most recently introduced forming the bottom of the pile,and removing boards from the top of the pile in the stacker, when thepile has reached a predetermined height, in amounts corresponding to thenumber of boards introduced to the bottom of the pile.

5. The method as claimed in claim 4 which includes the additional stepof controlling the rate of introduction and removal of boards from thebottom and top of the pile respectively to provide for treatment withinthe stackor equivalent to at least four hours at 260 F.

6. A hot stacker for use in conjunction for receiving boards while hotfrom a hot molding press in the manufacture of boards molded of fibrousmaterial and a thermosetting binder whereby the binder, during themolding operation, is advanced to a set but incomplete stage of curecomprising a vertical housing having heat insulating walls with anopening to discharge boards from its upper portion and an opening toreceive boards in its bottom portion and in which the openings aredimensioned to have a size and shape corresponding with the size andshape of the boards adapted to be advanced therethrough, shelvesextending horizontally into the opening at the underside of the housing,means mounting the shelves for shifting movement between normal positionwherein the shelves extend laterally into the opening for support ofboards contained within the housing and outwardly to a retractedposition out of the path of the boards, a heated platen dimensioned tocorrespond with said opening in the underside of the housing, means forbringing the housing shelves and platen together normally to positionthe platenas the bottom wall of the housing, and means responsive tomovement of said housing shelves and platen together for displacing theshelves towards retracted position and for returning said shelves tonormal position for supporting the boards within the housing in advanceof separation between the housing shelves and platen.

7. A hot stacker as claimed in claim 6 in which the shelves arechamfered throughout their lower edge portion and the upper edge portionof the plates are similarly chamfered to permit actuation of saidshelves to position of use for engaging the underside of the boards inadvance of movement of the plate to retracted position.

8. A hot stacker for use in conjunction with a hot molding press in themanufacture of boards molded of fibrous material and a thermosettingbinder wherein the binder during the molding operation is advanced to aset but incomplete stage of cure, comprising a housing formed of heatinsulating walls open at the top and at the bottom and dimensioned insize and shape to correspond to the length and width of the moldedboards adapted to be inserted therein, shelves extending horizontallyinto the opening at the underside of the housing, means mounting theshelves for shifting movement between normal position wherein theshelves extend laterally into the opening for support of boardscontained within the housing and outwardly to a retracted position outof the path of the boards, a heated platen dimensioned to correspondwith said opening in the underside of the housing, means for bringingthe housing and platen together normally to position the platen as thebottom wall of the housing, and means responsive to movement of saidhousing and platen together for displacing the shelves towards retractedposition and for returning said shelves to normal position forsupporting the boards within the housing in advance of separationbetween the housing and platen.

9. A hot stacker as claimed in claim 8 which includes feeding means incooperation with said platen for advancing boards into a properalignment thereon when in position for receiving the boards.

10. A hot stacker as claimed in claim 9 which includes stop meanscooperating with said feeding means for properly locating said boards onsaid platen during feeding operations.

11. A hot stacker as claimed in claim 8 which includes heating elementsin the insulated walls of the housing for maintaining a temperaturelevel within the stacker in excess of 250 F.

References Cited in the file of this patent UNITED STATES PATENTS1,339,564 Kinnear et a1 May 11, 1920 1,358,394 Redman Nov. 9, 19202,537,918 SkOOg Jan. 9, 1951 2,595,346 Federwitz May 6, 1952

